In order to align drill development efforts with enterprise-level lean initiatives, several lean drilling systems are being developed in a new category of drilling technology identified as “portable automation”. Characteristic of these drilling systems is a significant reduction in rigidity over previous drilling systems such as large floor-mounted automated drilling systems or power feed drill fixtures that clamp directly to aircraft structure and require operator repositioning of large, heavy equipment to the next location in which an opening is to be made. Consequently, the drill spindle that is positioned by these portable automation systems must be specifically developed to minimize size, weight and center of gravity in order to minimize the moment arm and corresponding deflection of the drilling system while maintaining advanced drilling features such as one-pass drill/countersinking, peck feed drilling and/or positive feed drilling.
Currently, openings may be made in a structure using one of three basic methods. According to the first method, openings may be drilled by hand (manually fed) and then countersunk by hand via a Microstop Cage. Alternatively, the openings may be drilled and countersunk to a shallow dimension and then finished by hand with a pistol grip drill motor or equivalent and a Microstop Cage. These types of openings may be located by any number of methods including but not limited to: pilot openings, manually located openings or using a fixture. According to the second method, a manual operation utilizes a much larger and heavier drill that is located and secured by rigid fixtures. This type of drill is known as “power feed” and automatically feeds the drill through the material. According to the third method, the openings are made using expensive floor-mounted, numerically-controlled machines. While attempts have been made to design a drill spindle which satisfies the requirements of these methods, each has disadvantages which drive the need for an application-specific solution.
The disadvantage of openings drilled by hand (manually fed) according to the first method above flows from the requirement that an operator manually manipulate a drill and then a countersink. As with most manual operations, quality and quantity are very operator-dependent. Producing openings via this process is also a large contributor to cumulative trauma injuries. The second method above may require that that operator manually move large, heavy drill spindles to each opening which is located by a fixture-type tool which is normally large and heavy. Should the location of a fastener opening require alteration, the fixture detail may require reworking or replacement. These types of drills may provide vary limited feed rate options and may be of a fixed nature (same feed rate for the entire operation). The third method above may have the disadvantage of requiring a large monument-type apparatus fixture which may require significant capital investment and floor space. These machines may also require large, complex, and very rigid fixtures to position the assembly precisely to the n/c machine. The dedicated nature of n/c machines and their associated programs requires that they be part-specific and require much time and expense before they can be used with another part or assembly.